bias in maternal reports of smoking during pregnancy associated with fetal distress

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Bias in Maternal Reports of Smoking During Pregnancy Associated With Fetal Distress Author(s): Matthew Wong and Gideon Koren Source: Canadian Journal of Public Health / Revue Canadienne de Sante'e Publique, Vol. 92, No. 2 (MARCH / APRIL 2001), pp. 109-112 Published by: Canadian Public Health Association Stable URL: http://www.jstor.org/stable/41993283 . Accessed: 18/06/2014 05:26 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. . Canadian Public Health Association is collaborating with JSTOR to digitize, preserve and extend access to Canadian Journal of Public Health / Revue Canadienne de Sante'e Publique. http://www.jstor.org This content downloaded from 188.72.126.41 on Wed, 18 Jun 2014 05:26:36 AM All use subject to JSTOR Terms and Conditions

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Page 1: Bias in Maternal Reports of Smoking During Pregnancy Associated With Fetal Distress

Bias in Maternal Reports of Smoking During Pregnancy Associated With Fetal DistressAuthor(s): Matthew Wong and Gideon KorenSource: Canadian Journal of Public Health / Revue Canadienne de Sante'e Publique, Vol. 92, No.2 (MARCH / APRIL 2001), pp. 109-112Published by: Canadian Public Health AssociationStable URL: http://www.jstor.org/stable/41993283 .

Accessed: 18/06/2014 05:26

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected].

.

Canadian Public Health Association is collaborating with JSTOR to digitize, preserve and extend access toCanadian Journal of Public Health / Revue Canadienne de Sante'e Publique.

http://www.jstor.org

This content downloaded from 188.72.126.41 on Wed, 18 Jun 2014 05:26:36 AMAll use subject to JSTOR Terms and Conditions

Page 2: Bias in Maternal Reports of Smoking During Pregnancy Associated With Fetal Distress

Bias in Maternal Reports of Smoking

During Pregnancy Associated With

Fetal Distress

Matthew Wong, MSc,1'2 Gideon Koren, MD1'4

ABSTRACT

Background: Studies examining the adverse effects of smoking during pregnancy commonly use maternal reports. We hypothesized that if an adverse event occurred during pregnancy, women may underreport smoking. This study looked for bias in maternal report of smoking if fetal distress occurs.

Methods: Data were collected prospectively from patients attending The MotheRisk Program who smoked during pregnancy, and were categorized by delivery outcome, maternal and neonatal characteristics, and the raw number of cigarettes smoked per day during pregnancy reported at clinic and at follow-up. The differ- ence between these two values was compared.

Results: 95 women had uneventful deliveries and 25 had fetal distress. Women who reported fetal distress decreased their report of smoking after delivery compared to their original report during pregnancy, whereas women with an uneventful labour did not (p=0.04).

Conclusions: Our results suggest that if an adverse pregnancy outcome occurs, mothers may tend to underreport their cigarette consumption.

ABRÉGÉ

Contexte : Les études des effets néfastes du tabac pendant la grossesse emploient com- munément les déclarations des mères. Nous avons supposé qu'en cas de réaction adverse durant la grossesse, les femmes pourraient avoir tendance à minimiser le degré de leur tabagisme. Notre étude visait à détecter un biais dans les déclarations, par les mères, de leur utilisation du tabac en cas de détresse foetale.

Méthode : Nous avons recueilli des données à des fins prospectives auprès de patientes du programme MotheRisk qui fumaient pendant leur grossesse, puis classé ces données en fonc- tion du résultat de l'accouchement, des carac- téristiques de la mère et du nouveau-né, ainsi que du nombre de cigarettes fumées par jour pendant la grossesse, selon les déclarations des mères à la clinique et lors du suivi. Nous avons ensuite comparé les écarts entre ces deux derniers chiffres.

Résultats : 95 femmes ont signalé un accouchement sans problème, et 25 un accouchement avec détresse foetale. Ces dernières ont fait état d'une moindre utilisa- tion de la cigarette après l'accouchement que durant la grossesse. Pour les femmes ayant accouché sans problème, le degré de taba- gisme déclaré est resté le même.

Conclusions : Nos résultats suggèrent que lorsqu'une réaction adverse se manifeste à l'issue d'une grossesse, les mères auraient ten- dance à minimiser leur degré de tabagisme.

Studies examining the potential adverse fetal effects of smoking during pregnancy commonly rely on maternal self-reports. In the event of negative results, researchers often cite underreporting as a potential source of bias.1 This can have a profound effect upon such studies, particularly evi- dent when maternal reports are compared with a biological marker. Studies compar- ing biochemical markers of smoking, such as serum or urine cotinine levels, with maternal report of smoking found that between 5 and 15% of women who identi- fied themselves as nonsmokers had levels consistent with active smoking.2"4

The use of biological markers, however, is not always feasible for several reasons including reluctance of patients to give consent, which itself can introduce bias, and in the case of retrospective studies where only patient records are available. Moreover, the existing studies,2 4 while identifying a reporting bias of smoking dichotomously (i.e., "yes" versus "no"), were not designed to address a bias in the number of cigarettes reported.

At least two reasons for underreporting have been suggested. First, because of diminishing social acceptance of smoking during pregnancy, mothers may provide false reports of their smoking, believing

1 . The Faculty of Pharmacy, University of T oronto, Toronto, ON

2. The Division of Clinical Pharmacology/ Toxicology, The Hospital for Sick Children, Toronto

3. The MotheRisk Program, The Hospital for Sick Children, Toronto

4. The Departments of Pediatrics, Pharmacology, and Medicine, University of Toronto Correspondence and reprint requests: Gideon Koren, The Division of Clinical Pharmacology and Toxicology, The Hospital for Sick Children, 555 University Ave., Toronto, ON, M5G 1X8, Tel: 416- 813-5781, Fax: 416-813-7562 Supported in part by the Medical Research Council of Canada, and the Seed Grant Program, The Hospital for Sick Children.

them to be more socially acceptable to the researchers.5 Second, in the instance of an adverse event during pregnancy or deliv- ery, women may underreport a behaviour that they associate with these adverse events. This has never previously been demonstrated empirically.

It is well accepted that smoking during pregnancy puts the fetus at an increased health risk. Studies have clearly illustrated the increased risk for lower birthweight, perinatal mortality and delivery complica- tions.6'7 These risks are often explained to women who smoke during their pregnancy by health professionals, and these women are often cited as being aware of these risks prior to counselling.8

The objective of the present study was to investigate whether there is bias in mater- nal report of the amount of cigarette con- sumption if fetal distress is diagnosed. Fetal distress is described as a cluster of clinical situations, including oxygen depri- vation (e.g., presence of meconium, low Apgar score), heart rate abnormality or biochemical disturbances (e.g., fetal acidemia).9"11 Fetal distress presented at birth often requires medical interventions, and these infants may suffer long-term sequelae.12 Although fetal distress is lacking an accurate clinical definition, most moth- ers are aware of it and report it.

METHODS

The original data on smoking status were collected prospectively from patients seen between 1988 and 1997 in clinic by a physician through The MotheRisk Program (The Hospital for Sick Children, Toronto, Ontario, Canada) - a counselling service for women with medicinal, chemi- cal, illicit drug or other exposures in preg- nancy. The majority of patients are from a middle to upper socioeconomic category,

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BIAS IN MATERNAL REPORTS OF SMOKING

TABLE I Additional Information Provided by Mothers Reporting "Fetal Distress"

Comment No. of Occurrences*!- Emergency Caesarian

Section Performed 6 Baby's Heart Rate was Low 5 Cord Around Neck 4 Baby's Heart Rate Elevated 3 Induced Labour 3 Baby Admitted to NICU 2 No Additional Comments* 2 Decreased Oxygen to Fetus 1 Presence of Meconium 1 Baby Aspirated Meconium 1 "Baby was Blue" 1 Baby Received Oxygen 1 * 2 women did not elaborate on the circum-

stances of Fetal Distress t Not mutually exclusive

representing the diverse ethnic background found in the greater Toronto area. During the clinic visit, maternal characteristics including age, gravidity, parity, and previ- ous spontaneous or therapeutic abortions were collected as were details of underlying medical condition and previous pregnancy outcomes. Detailed reports of patient exposures during pregnancy were made ascertaining time of exposure, dose and fre- quency of use, where applicable. These included exposures that the patient had come to clinic for specifically, as well as other exposures including cigarettes, alco- hol and illicit drugs.

After collection of all data, patients were explained the concept of a baseline risk that exists in every pregnancy for an infant to have a major birth defect without any ter- atogenic exposure. Through critical evalua- tion of the current medical literature, patients were then informed of the potential risk (if any) to the fetus as a result of these exposures. Treatment for any substance use issues, or other therapeutic intervention occurs through referral, or direction back to the primary physician. Documentation of the counselling with specific literature refer- ences is then forwarded to the physician car- ing for the woman and also to the patient directly if requested.

As part of the research program, patients seen in clinic may be followed up with a telephone interview within two years after their clinic visit to confirm exposure details and to inquire about pregnancy outcome.

For the present study, patients were selected based on three criteria: 1) Live

birth with completion of the follow-up interview, 2) documented delivery details, and 3) documented details of maternal smoking behaviour in both clinic and follow-up files (a value of zero could occur in either the clinic or follow-up file, but zero in both files by definition was a non- smoker). Exclusion was based on docu- mentation in the files of intentional decrease or cessation of smoking (where the patient record documented an alter- ation in behaviour, e.g., "cut down" or "quit/quitting"), or where details of smok- ing were not complete for clinic or follow- up information (e.g., 16 cigarettes per day at clinic vs. response of only "yes" at follow-up). During follow-up interviews, patients were asked if there was an event of "Fetal Distress" during delivery and the interviewer gave examples summarized in Table I. The mother's response to this question was documented in a narrative. Patients were categorized into one of two groups based on their report of "Fetal Distress" or "Uneventful Delivery".

These two groups were then compared regarding maternal characteristics at clinic, number and nature of exposures (terato- genic, unknown, nonteratogenic), use of alcohol or illicit drugs, presence of mater- nal illness, and incidents of fetal distress in a previous delivery. Neonatal characteris- tics at follow-up including gestational age, birth weight and presence of major malfor- mations, and time between clinic visit and follow-up were also compared. Comparisons between the two groups were done using the Student's t-test, Mann- Whitney Rank Sum Test or Chi-square as appropriate.

The primary endpoint of interest was the difference in the reported daily number of cigarettes in the first trimester between the first interview ("real time") versus the second (post partum) interview. The raw number of cigarettes smoked per day reported at clinic, at follow-up and the dif- ference between the two values (follow-up value minus clinic value) were compared between women reporting "Fetal Distress" versus "Uneventful Delivery" using the Mann-Whitney Rank Sum Test. The numerical difference in number of ciga- rettes per day reported in the second versus the first interview was then categorized as

having increased (positive value), remained the same (zero value), or decreased (nega- tive value) and were compared using the Chi-squared test.

RESULTS

From 2,432 patients seen in clinic, 379 patients were identified with smoking reported, and 205 were selected for research-related follow-up. Seventeen patients refused the follow-up interview and 56 were "lost to follow-up". In total, 132 cases remained which met the inclu- sion criteria. However, in 7 cases patients expressly mentioned that they had quit, and in 2 cases mentioned successfully decreasing their smoking. In 2 cases data were not sufficiently quantified to be ana- lyzed and in 1 case the patient told the interviewer that she had "memory prob- lems". After exclusions, there were 120 eli- gible cases. Of these 120 women, 95 reported an uneventful delivery and 25 reported an event following the definition of "Fetal Distress". These women provided details of the events in narratives summa- rized in Table I.

Maternal characteristics at clinic between women who had an uneventful delivery and those who had "Fetal Distress" were not significantly different (Table II), including maternal age, gravidity, parity, and spontaneous or therapeutic abortions. The mean number of exposures to terato- genic or nonteratogenic agents did not dif- fer. Use of illicit drugs or alcohol during pregnancy also did not differ between the two groups, nor did the proportion of women who had a chronic illness, includ- ing psychiatric illness. Finally, there were no significant differences in the proportion of women who had an event of "Fetal Distress" during a previous pregnancy.

Other than the selection criteria of "Fetal Distress", pregnancy outcome char- acteristics at follow-up also did not differ significantly between the two groups as shown in Table III. There was no differ- ence between the two groups in the pro- portion of infants born with major malfor- mations, in gestational age at birth, or birth weight. In addition, there was no sig- nificant difference in the number of months that had elapsed between clinic

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BIAS IN MATERNAL REPORTS OF SMOKING

TABLE II

Maternal Characteristics at Clinic Uneventful Delivery "Fetal Distress" P value

n=95 n=25 Maternal Age* 29.1 ±4.9 31 .0±4.9 0.09+ Gravidity"}" 2 [1-7] 1 [1-6] 0.1 61 Parity! 1 [0-4] 0 [0-5] 0.1 21 SAt 0 [0-6] 0 [0-2] 0.821 TAt 0 [0-2] 0 [0-2] 0.851 No. Exposures for Clinicf 1 [1-7] 2 [1-8] 0.611 No. Exposures Teratogenict 0 [0-1] 0[0-1] 0.991 No. Exposures Unknownf 0 [0-3] 0 [0-2] 0.651 No. Exposures Nonteratogenicf 1 [0-7] 1 [0-8] 0.81 1 Use of Illicit Drugs 11(11 .6%) 3 (1 2%) 0.77§ Use of Alcohol 37 (38.9%) 1 4 (56%) 0.1 9§ Maternal Illness 72 (75.8%) 18 (72%) 0.90§ Psychiatric Illness 27 (28.4%) 6 (24%) 0.85§ Prev. "Fetal Distress" 0 (0%) 1 (4%) 0.47§ * Values expressed as mean ± S.D. t Values expressed as median with range $ Student's t-test 1 Mann-Whitney Rank Sum Test § Chi-squared

TABLE III Follow-up Characteristics

Uneventful Delivery "Fetal Distress" P value n=95 n=25

Major Malformations 3(3.2%) 0(0%) 0.86§ Gestational Age (wk)t 40 [35-42] 40 [34-42] 0.501 Birthweight (g)* 3271 ±546 3250±565 0.86* Time to Follow-up (mos)t 16 [7-35.5] 20 [2-36.5] 0.311 * Values expressed as mean ± S.D. t Values expressed as median with range $ Student's t-test 1 Mann-Whitney Rank Sum Test § Chi-squared

TABLE IV Maternal Self-Report of Smoking

Uneventful Delivery "Fetal Distress" P value n=93 n=25

No. Cig/d reported at Clinicf 10 [0-40] 10 [0-30] 0.281 No. Cig/d reported at Follow-upt 10 [0-40] 10 [0-25] 0.71 1 Difference in No. Cig/d reported

at Follow-up vs. Clinict 0 [-24-+30] -4[-10-+15] 0.041

t Values expressed as median with range 1 Mann-Whitney Rank Sum Test

TABLE V Changes in Self-Report of Maternal Smoking

Change in No. Cig/d Uneventful Delivery "Fetal Distress" P value Reported at Follow-up n=95 n=25 vs. Clinic

Increased 24 (25.3%) 5 (20%) 0.02§ Same 34(35.8%) 3(12%) Decreased 37 (38.9%) 1 7 (68%) § Chi-squared

visit and follow-up between the two groups.

Details of maternal self-report of smok- ing are shown in Table IV. There was no

significant difference in the number of cig- arettes smoked per day during pregnancy reported at clinic between the two groups. There was also no significant difference

(p=0.32) in the proportion of mothers who at follow-up declared themselves to be non-smokers (decreased to zero cigarettes). There was however a statistically signifi- cant difference between the two groups in the change of report for cigarette con- sumption during pregnancy at clinic versus follow-up after pregnancy. That is, moth- ers who experienced Fetal Distress in their babies reported significantly less smoking during pregnancy at follow-up than during their initial clinic visit. This difference was categorized, shown in Table V. The two groups were significantly different in terms of the change in the report of number of cigarettes per day at follow-up with respect to whether it had increased, remained unchanged or decreased. These results indicate that mothers who had events of fetal distress during delivery were signifi- cantly more likely to decrease their subse- quent report of smoking during pregnancy compared to mothers who had uneventful deliveries, who did not change their reports.

DISCUSSION

The problem of underreporting in epi- demiological research poses a threat to the validity of a study. Our results suggest that in studies of adverse outcomes during pregnancy, mothers tend to underreport their smoking.

Because the study groups had similar characteristics and outcomes, it is highly probable that the adverse pregnancy out- come led to the reporting bias. Moreover, women with uneventful pregnancies did not change their reported number of ciga- rettes (median change=0), indicating that because of the chronic and stable nature of smoking, there is no problem of recall per se.13 The event of fetal distress may have in fact improved maternal recall. In a study examining bottled water consump- tion during pregnancy, women who had spontaneous abortions had a more accu- rate recall of their water intake when com- pared to women with uneventful out- comes.14 Again, this is not an issue of recall per se, but rather of recall bias.

The present study has two major advan- tages over previous attempts to characterize reporting bias: This was a prospectively

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collected cohort, and at the time of the ini- tial interview, women had significant incentives to be very open about their smoking habits. Also, assessment of changes in the number of reported ciga- rettes was possible.

A potential limitation of this study is generalizability. This research examined differences in reports relative to an initial reported value. Reliability of the initial report, and the extent of subsequent underreporting may differ between popula- tions. Patients attending the MotheRisk program are highly motivated. It is assumed that the majority of these women provide complete and accurate informa- tion, in order to receive a more accurate risk assessment. In a population with no incentive for accurate reporting, the initial report could be less reliable. The extent of underreporting occurring after fetal distress may depend on a number of variables. Maternal guilt may result in an attempt to conceal behaviour, or may encourage com- plete divulgence. With our data, some of the incentives for maternal truthfulness may be lost postpartum, and it is unknown whether the postpartum report in our study population would be more or less reliable than a report in another popula- tion.

The results of this study reinforce the need to obtain biological markers of expo-

sures during pregnancy. However, while biological markers can help distinguish smokers from nonsmokers, they may not be adequate for the detection of changes in consumption, as nicotine undergoes phar- macokinetic changes during pregnancy.15

Further studies in the area of under- reporting should be undertaken to deter- mine if there is some predictive value that can be gained from these results. Many studies categorize smoking behaviour as "light" versus "heavy", based on a value of 10 or more cigarettes per day. Four ciga- rettes per day could indeed affect that cate- gorization and bias study results. If there is a consistent pattern of underreporting or determinants of underreporting, this would be important information in an attempt to improve the understanding of the maternal fetal toxicology of tobacco smoke.

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Received: December 1, 1999 Accepted: September 7, 2000

Tobacco , from page 89

of the tobacco industry in orchestrating the smuggling that ensued have now been brought to light. Lack of progress on ciga- rette taxes and other key tobacco control measures, such as increased restrictions on smoking in public places and workplaces, is due to industry lobbying, lack of public concern, political ideology, and other political factors.

While the role of the state in public health and some of the concerns raised by Fischer and Rehm are worthy of further debate, we hope that such debate will not delay the implementation of measures that are known to be effective. Litigation can

play an important role in holding the tobacco industry accountable for its contri- bution to the continuing epidemic of tobacco-related disease and death.

The opinions expressed in this article are those of the authors and not of their respective institutions.

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